On Friday night, she appeared in Cleveland with music power couple Jay-Z and Beyonce.

Speaking to the crowd, Beyonce - whose dancers all wore 'I'm with her' T-shirts - shared an impassioneed speech, saying she would like to see daughter Blue grow up seeing a "woman lead our country and know that her possibilities are limitless".

The singer is a staunch supporter of Clinton (Image: Getty)

"Less than 100 years ago women did not have the right to vote," the mum-of-one said. "Look how far we've come from having no voice to being on the brink of making history - again - by electing the first woman president. But we have to vote.

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"The world looks to us as a progressive country that leads change. Eight years ago I was so inspired to know that my nephew, a young black child, could grow up knowing his dreams could be realised by witnessing a black president in office.

"And now we have the opportunity to create more change. I want my daughter to grow up seeing a woman lead our country and know that her possibilities are limitless.

(Image: Getty)

(Image: AFP/Getty Images)

(Image: AFP/Getty Images)

"We have to think about the future of our daughters, our sons, and vote for someone who cares for them as much as we do. And that is why I'm with her."

In response, Hillary said: "When I see them, hear this passion and energy and intensity, I don't even know where to begin. Because this is what America is, my fiends."

Opinion polls show Clinton still holds advantages over her Republican rival, Donald Trump, in states that could be critical in deciding the election.

But her lead has narrowed after a revelation a week ago that the Federal Bureau of Investigation was looking into a new trove of emails as part of its probe into her handling of classified information while she was secretary of state.